OF THE FAMILY BACILLARIA. 123 



scope. The forms, as usually seen, appear tabular, but when 

 thrown on their sides by means of a compressor, they show con- 

 siderable thickness. 



I have noticed in several species groups of molecules moving 

 actively, precisely like those seen in Closterium. Indeed this 

 genus is most closely allied to Closterium, and some forms occur 

 which show a complete transition from one genus to the other, 

 (See remarks under the head, Closterium.) 



Capt. Carmichael, with his usual acuteness, detected their ani- 

 mal nature. He remarks of two of the species, " these are ani- 

 mals instead of plants, if the faculty of locomotion will entitle 

 them to that rank." (See Hooker's British Flora, V. p. 398.) I 

 have frequently noticed the motion of several species ; it is quite 

 as distinct in Closterium. 



1. Euastnim rota, Ehr. (Fig. 22, PL I.) Body binaiy, lenticular, 

 discoid, smooth, the edges dentate or spiny, one twenty-fourth toons 

 tenth of a line. Echinella rotata ? Greville. 



The species represented in our figm*e appears to be the E. rota 

 of Ehrenberg, and agi-ees pretty well with the account given by 

 Greville of his Echinella rotata, which he describes as having 

 the " frond plane, cu'cular, divided by a line passing through the 

 centre, each portion composed of radiating segments cleft nearly 

 to the central line." (See Brit. Flora, V. p. 398.) Having seen 

 no figures of the European species, I cannot be sure of their 

 identity with ours. 



The species represented in fig. 22, is quite common in the 

 United States. I have seen it in Rhode Island, New York, Vir- 

 ginia, and Ouisconsin ; I have generally found it scattered among 

 Conferva, but I once, in early spring, found man/i/ hundreds of 

 them collected together on the bottom of a very small pool of 

 water in a sphagnous bog. Some variety occurs in the outline ; 

 thus the two large central portions of each half are often -perfectly 

 symmetrical, and not unfrequently dentate near tlie ends. I have 

 seen specimens twice the size of the one represented. 



2. Euastrum crux melitensis. (Fig. 23? PI. I.) Body binary, len- 

 ticular, discoid, smooth, the edges deeply divided into six dentate and 

 spmy rays. 



